The events leading up to the video are as follows. One of the student groups at Middlebury College is called The American Enterprise Club. According to its website, the Club aims “to promote … free enterprise, a limited federal government, a strong national defense.” In other words, it’s a group for political conservatives.

This year, the AEI Club invited Dr. Charles Murray to speak. That’s crucial to understanding what followed. When leftists protest right-wing speakers on campus, they often deny that they are infringing upon free speech. Free speech, they insist, does not require their university to give a platform to people with offensive views. That was the argument of the people who earlier this year tried to prevent ex-Breitbart writer Milo Yiannopoulos from speaking at the University of California at Berkeley. And it was the argument of those who opposed Murray’s lecture at Middlebury. “This is not an issue of freedom of speech,” declared a letter signed by more than 450 Middlebury alums. “Why has such a person been granted a platform at Middlebury?”

The answer is that Middlebury granted Murray a platform because a group of its students invited him. Those students constitute a small ideological minority. They hold views that many of their classmates oppose, even loathe. But the administrators who run Middlebury, like the administrators who run Berkeley, consider themselves obligated to protect the right of small, unpopular, minorities to bring in speakers of their choice. Denying them that right—giving progressive students a veto over who conservative students can invite—comes perilously close to giving progressive students a veto over what conservative students can say. If it is legitimate for campus progressives to block speeches by Milo Yiannopoulos or Charles Murray, why can’t they block speeches by fellow students who hold Yiannopoulos or Murray’s views?

Some of Murray’s views are indeed odious. Twenty-three years ago, he co-authored The Bell Curve, which argued that differences in intelligence account for much of the class stratification in American life, that intelligence is partly genetic, and that there may be genetic differences between races. Critics called Murray’s argument intellectually shoddy, racist and dangerous, and I agree. (Before I began working there full-time, my old magazine, The New Republic, published an excerpt of the book, along with rebuttals, and thus gave it a legitimacy it did not deserve).

But if conservative students cannot invite speakers who hold what I and many other liberals consider reprehensible views, then they cannot invite many of the most prominent conservative thinkers and Republican politicians in the United States today. Like many liberals, I consider it bigoted to oppose gay marriage. I consider it bigoted to support voting restrictions that disproportionately impact African Americans and Latinos. I consider it bigoted to deny trans students the right to use the bathrooms of their choice. I consider it bigoted to claim that Islam is inherently more violent than Judaism or Christianity. I consider it unconscionable to oppose government action against climate change.

Yet on the American right, these views are all mainstream. If conservative students can’t bring Charles Murray to Middlebury, how can they bring Ted Cruz, Newt Gingrich or Clarence Thomas? (Indeed, Yiannopoulos and Murray aren’t the only right-leaning speakers who have sparked mass student protest in recent years. So have Condoleezza Rice and International Monetary Fund head Christine Lagarde).

In fact, Middlebury students did not only object to Murray because of The Bell Curve. Some also objected to his most recent book, Coming Apart, which analyzes the struggles of the white working class. (And about which Murray was scheduled to talk). Coming Apart, declared a group called White Students for Racial Justice, “uses largely anecdotal evidence to blame poor people in America for being poor, attempting to explain economic inequality through a perceived gap in virtue” and thus proves that Murray is “classist.”

The point is this. What’s considered morally legitimate at Middlebury differs dramatically from what’s considered morally legitimate in large swaths of America. When colleges like Middlebury are considering whom to honor, they have every right to apply their own ideological standards. But if they use those standards to determine which speakers conservative student groups can invite, they will make it hard for those groups to function on liberal campuses at all. And in an era in which Americans are already ideologically cocooned, that would be a disaster.

To appreciate the ugliness of what transpired at Middlebury, however, one needs to look not merely at the principles involved, but at the specific sequence of events. In its letter to the campus explaining its invitation to Murray, the AEI club declared that it “invites you to argue.” It invited a left-leaning Middlebury professor, Allison Stanger, to engage Murray in a public conversation following his talk, thus ensuring that his views would be challenged. In his introduction to Murray’s speech, a representative from the AEI club implored his fellow students to debate Murray rather than shouting him down.

But they did shout him down. As Murray approached the podium, dozens of students in the audience turned their backs, loudly read a prepared statement, and then began chanting “Hey, hey ho ho, Charles Murray has got to go,” “Your message is hatred, we cannot tolerate it” “Charles Murray go away, Middlebury says no way” and finally, “Shut it down.”

After close to twenty minutes of this, a university representative came on stage to announce that, if the students did not relent, Murray and his interlocutor, Professor Stanger, would move to a secret location, from which their conversation would be broadcast. Professor Stanger then took the microphone and asked the students, “Can you just listen for one minute.” Many in the audience replied, “no.” She added that, “I spent a lot of time preparing hard questions.” Finally, she conceded that, “You’re not going to let us speak.” As the university representative announced that Murray and Stanger would move to a different location, the crowd began shouting, “Where are you going?”

Somehow, they found out. Because when Murray and Stanger finished their dialogue, they found themselves surrounded by protesters. The protesters—some of whom were wearing masks and may not have been Middlebury students—began pushing them. When Stanger tried to shield Murray, according a Middlebury spokesman, a protester grabbed her hair and twisted her neck.

Murray, Stanger and their escorts made it to a waiting car, but the protesters

Finally, Murray and Stanger got away. They had planned to eat dinner at a local restaurant, but, upon learning that the protesters planned to disrupt their meal, left town altogether. Stanger later went to the hospital, where she received a neck brace.

This is not a tale of university cowardice. To the contrary, the Middlebury administration took extraordinary measures to ensure that Murray could speak. And in a letter following the incident, President Laurie Patton, declared that in their response to Murray’s speech, some Middlebury students “failed to live up to our core values.” She publicly apologized to Murray.

Still, that’s not enough. College policy declares that, “Middlebury College does not allow disruptive behavior at community events or on campus.” Many of the students protesting Murray’s speech clearly violated that policy. I hope they are punished. If they are, perhaps progressive students will think twice before shouting down a conservative speaker the next time.

Liberals may be tempted to ignore these incidents, either because they are uncomfortable appearing to defend Charles Murray, or because, in the age of Donald Trump, they’re worried about bigger things. That would be a mistake. If what happened at Berkeley, and now at Middlebury, goes unchallenged, sooner or later, liberals will get shouted down too. To many on the campus left, after all, Zionism is a racist ideology. Drone attacks constitute war crimes. Barack Obama was the deporter-in-chief. Hillary Clinton supported a racist crime bill. Joe Biden disrespected Anita Hill. There will always be justifications.

Professor Allison Stanger is a liberal. Last week she ended up in a neck brace merely for being willing to ask Charles Murray hard questions. She should serve as an inspiration, and a warning of things to come.

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Peter Beinart is a contributing editor at The Atlantic and a professor of journalism and political science at the City University of New York.